Requirements for controller integration/support for MySensors?

@hek What are the requirements to get a controller fully supported by MySensors?
I mean technically and API wise. My friend is producing the Cozify controller and planning to open APIs for custom sensor development like MySensors.

Well, the controller must support one or more ways of communicating with the MySensors gateway (serial, ethernet, MQTT). Allowing multiple "gateways" is preferred, as many users deploy ESP8266 nodes with sensors directly attached to the esp.

The controller has to support the id-hand-out mechanism for the nodes. Then you have to implement as many MySensors device-types as possible for the new controller. Start with the simple and most used, such as Binary, Dimmer, Temp and Humidity.